1. Field of the Invention
The present invention relates to a rubber laminate and a pneumatic tire using the same, more particularly relates to a rubber laminate making improvements in the bonding rubber layer used between a hydrogenated NBR composition and a general diene-based rubber and a pneumatic tire using the same.
2. Description of the Related Art
The present inventors took note of the usefulness of hydrogenated NBR compositions and previously provided various rubber products by laminating them with general diene-based rubbers. Such hydrogenated NBR compositions, however, suffer from a problem in respect to the bondability with general diene-based rubbers. The inventors have proposed several effective bonding rubber compositions for improving the bondability (Japanese Unexamined Patent Publication (Kokai) No. 11-100463, Japanese Unexamined Patent Publication (Kokai) No. 11-116735, etc.) In the case of a run-flat tire etc. using a hydrogenated NBR composition for the reinforcing liner of the tire, however, since the tire is used at extremely high temperatures and under high strain, the previously proposed bonding rubber compositions were still insufficient in terms of bondability. For example, the running performance at the time of a flat tire (run-flat performance) was insufficient.
An object of the present invention is to provide a rubber laminate greatly improving the bonding strength at a high temperature and under high strain by adjusting the formulation of the bonding rubber arranged between a hydrogenated NBR composition and general diene-based rubber and a pneumatic tire using the same.
According to a first aspect of the present invention, there is provided a rubber laminate comprising a rubber composition (A), obtained by blending 0 to 120 parts by weight of zinc methacrylate and an organic peroxide into a total of 100 parts by weight of rubber ingredients including at least 40 parts by weight of an ethylenic unsaturated nitrile conjugated diene-based high saturation rubber with a content of conjugated diene units of not more than 30 wt %, and a sulfur-vulcanizable diene-based rubber composition (B) bonded by vulcanization through a bonding rubber composition (C), wherein the bonding rubber composition (C) is comprised of 100 parts by weight of a rubber containing 50 to 85 parts by weight of at least one type of diene-based rubber selected from natural rubber, polyisoprene rubber, polybutadiene rubber, and a conjugated diene-aromatic vinyl copolymer and 15 to 50 parts by weight of the ethylenic unsaturated nitrile-conjugated diene-based high saturation rubber with a content of conjugated diene units of not more than 30 wt % plus 10 to 60 parts by weight of zinc methacrylate, 0.3 to 10 parts by weight of an organic peroxide, and 5 to 50 parts by weight of a co-cross-linking agent having one of an acryl group, methacryl group, and allyl group and liquid at room temperature.
Preferably, the co-cross-linking agent is an aromatic ester having an allyl group.
More preferably, in the bonding rubber composition (C), first the ethylenic unsaturated nitrile-conjugated diene-based high saturation rubber with a content of conjugated diene units of not more than 30 wt % is mixed with the zinc methacrylate and then this composition is mixed with the diene-based rubber and other compounding agents.
Still more preferably, the bonding rubber composition (C) includes 5 to 50 parts by weight of an aromatic petroleum resin having an average molecular weight of 300 to 1500, a softening point of 50 to 160xc2x0 C., and an iodine absorption value of at least 20 g/100 g.
According to a second aspect of the invention, there is provided a pneumatic tire using the above rubber laminate.
According to a third aspect of the present invention, there is provided a safety tire using the rubber composition (A) for a crescent-shaped reinforcing rubber layer of a side part and arranging around it the bonding rubber composition (C) of an average thickness of 0.2 to 1.5 mm.
According to a fourth aspect of the present invention, there is provided a safety tire having a run-flat performance using the rubber composition (A) for a crescent-shaped reinforcing rubber layer of a side part and an inner liner and arranging the bonding rubber composition (C) of an average thickness of 0.2 to 1.5 mm between them and a carcass.